A spectrum in which a serving cell of a Long Term Evolution (LTE) system is located is a licensed spectrum, and can be used by only an operator network with the purchased licensed spectrum. At present, the industry increasingly concerns an unlicensed spectrum. Carrier aggregation is performed on an unlicensed spectrum that is used as a secondary carrier and a licensed spectrum that is used as a primary carrier, to serve user equipment (UE). This is the most concerned method for using an unlicensed spectrum at present. The secondary carrier corresponding to the unlicensed spectrum may be referred to as an unlicensed secondary carrier, and the primary carrier corresponding to the licensed spectrum may be referred to as a licensed primary carrier.
The unlicensed spectrum may be used as the secondary carrier to transmit data for UE. However, the unlicensed spectrum may be discontinuous. A base station can only use the unlicensed spectrum for a specific time period after obtaining a resource of the unlicensed spectrum by means of contending. After another base station occupies the unlicensed spectrum by means of contending, when the another base station occupies the unlicensed spectrum, the base station cannot send a signal by using the unlicensed spectrum. The base station cannot send a signal to UE by exclusively using the unlicensed spectrum. Therefore, the unlicensed spectrum can be used only as a secondary carrier to provide a service for user equipment. The unlicensed spectrum needs to be anchored to a licensed spectrum for using. For example, the unlicensed secondary carrier needs to be anchored to a licensed primary carrier for using. In this case, the primary carrier and the secondary carrier need to have a same timing relationship, a same subframe number, and a same subframe boundary.
The unlicensed spectrum refers to a public spectrum that any organization or person can use. However, a specific rule needs to be followed in use, for example, listen before talk (LBT). That is, only when it is determined, by means of listening, that the spectrum is idle, a signal can be sent on the unlicensed spectrum. Generally, clear channel assessment (CCA) or extended CCA (ECCA) is used in LBT. A channel is listened for at least 20 μs for a base station in CCA. If a signal is not obtained by means of listening, the channel is considered to be idle and can be used. If the base station finds, after performing listening for 20 μs, that the channel is occupied, CCA is switched to ECCA. A random number R is generated for the base station in ECCA, and the channel is listened in continuous R time periods. If the channel is all in an idle state in the R time periods, the channel can be used. An end time of CCA or ECCA may be a symbol at the middle of a subframe of the unlicensed spectrum. Therefore, data cannot be transmitted at subsequent several symbols. This causes a waste of spectrum resources.